1. Field of the Invention
This invention relates to an improved actuating mechanism for ball valves, particularly the type that are employed in subterranean wells.
2. Description of the Prior Art
A ball valve which is rotatable between an open and closed position with respect to a fluid conduit is employed in many industrial applications, but finds particular utility when employed as a safety valve in a subterranean well. The typical ball valve has a cylindrical flow passage through its center and is rotatable between an open position, wherein the flow passage is aligned with the fluid conduit in which the ball valve is mounted, and a closed position wherein the fluid passage is disposed transversely with respect to the bore of the fluid conduit. To prevent leakage around the exterior of the ball in its closed position, it is common to provide a so-called flow tube which carries in its end an annular seal for sealingly engaging the periphery of the ball in its closed position. Appropriate seals are provided for effecting the sealed engagement of the flow tube in the tubular conduit, hence fluid leakage around the exterior of the ball in the closed position is effectively prevented.
It has long been recognized that it is desirable to remove the annular seal carried by the flow tube from pressured engagement with the ball surface prior to effecting rotational movement of the ball. See for example, U.S. Pat. No. 4,293,038 to Evans, wherein a single angular piston is employed to axially shift an actuating sleeve which first engages the ball sealing elements of the flow tube to move them out of engagement with the ball surface and then a cam slot in the actuating sleeve engages the ball rotation pins to effect the rotation of the ball to its open position.
The use of a conventional annular flow tube mechanism does have certain disadvantages, however. In the first place, through the employment of an annular piston, which necessarily must be of greater internal diameter than the bore of the flow conduit, relatively expensive and short-lived sealing elements must be employed to effect the necessary seals around the piston to insure its actuation by an applied control fluid pressure. Additionally, the utilization of a common piston to first shift the flow tube away from the ball and then to rotate the ball has the disadvantage that any jamming of the flow tube will prevent the ball from being rotated.